DC-coupled differential circuit front end

Patent metadata

Field	Value
Publication number	US-9306609-B1
Application number	US-201514595303-A
Country	US
Kind code	B1
Filing date	Jan 13, 2015
Priority date	Jan 13, 2015
Publication date	Apr 5, 2016
Grant date	Apr 5, 2016

Abstract

A front-end of a first differential circuit is DC-coupled to a second differential circuit. The front-end comprises a resistive element, a voltage sensor and a current adjustor. The resistive element has a resistivity between a first end that is DC-coupled to the second circuit and a second end that is DC-coupled to the first circuit and accepts a programmable current passing therethrough to impose a voltage across the element that varies in direction and amplitude according to the current value. The voltage sensor senses a difference between a DC voltage at the second end of the resistive element and a desired reference voltage of the first circuit. The current adjustor adjusts a direction and amplitude of the programmable current so that the voltage of the first circuit matches the desired reference voltage of the first circuit. The first circuit may be a receiver circuit and the second circuit may be a transmitter circuit. The front-end may further comprise a current canceller comprising a second resistive element connected at a first end to the output of the second circuit. The current canceller senses the programmable current and generates a current of equal amplitude through the second resistive element and away from the output of the second circuit. The current canceller may be implemented in digital or analog form and/or in differential or common-mode operation.

First claim

What is claimed is:

1. A front-end of a first differential circuit that is DC-coupled to a second differential circuit, comprising:
a resistive element, having a resistivity between a first end that is DC-coupled to the second circuit and a second end that is DC-coupled to the first circuit, for accepting a programmable current passing therethrough to impose a voltage thereacross, that varies in direction and amplitude according to the current value;
a voltage sensor for sensing a difference between a DC voltage at the second end of the resistive element and a desired reference voltage of the first circuit; and
a current adjustor for adjusting a direction and amplitude of the programmable current so that the DC voltage of the first circuit matches the desired reference voltage of the first circuit.

2. A front-end according to claim 1 , wherein the first circuit is a receiver circuit.

3. A front-end according to claim 1 , wherein the second circuit is a transmitter circuit.

4. A front-end according to claim 1 , wherein the resistive element is a resistor.

5. A front-end according to claim 1 , wherein the voltage sensor comprises a comparator for comparing the DC voltage with the desired reference voltage.

6. A front-end according to claim 1 , wherein the current adjustor comprises a current source.

7. A front-end according to claim 6 , wherein the current source generates current if the desired reference voltage is greater than the DC voltage.

8. A front-end according to claim 7 , wherein an amplitude of the current generated by the current source increases in proportion to an amount the desired reference voltage exceeds the DC voltage.

9. A front-end according to claim 7 , wherein an amplitude of the current generated by the current source decreases in proportion to an amount the desired reference voltage is exceeded by the DC voltage.

10. A front-end according to claim 6 , wherein the current source is positioned between a positive DC voltage and the second end of the resistive element.

11. A front-end according to claim 6 , wherein the current source comprises a digital-to-analog converter (DAC) for outputting a current value in response to a digital current input value.

12. A front-end according to claim 1 , wherein the current adjustor comprises a current sink.

13. A front-end according to claim 12 , wherein the current sink sinks current if the desired reference voltage is less than the DC voltage.

14. A front-end according to claim 12 , wherein an amplitude of the current sunk by the current sink decreases in proportion to an amount the desired reference voltage exceeds the DC voltage.

15. A front-end according to claim 12 , wherein an amplitude of the current sunk by the current sink increases in proportion to an amount the desired reference voltage is exceeded by the DC voltage.

16. A front-end according to claim 12 , wherein the current source is positioned between the second end of the resistive element and a reference ground.

17. A front-end according to claim 12 , wherein the current sink comprises a digital-to-analog converter (DAC) for outputting a current value in response to a digital current input value.

18. A front-end according to claim 1 , wherein the current adjustor comprises a feedback control circuit for controlling an amount and direction of current generated in response to a comparison between the desired reference voltage and the DC voltage.

19. A front-end according to claim 18 , wherein the feedback control circuit accesses the voltage sensor and current adjustor in a common-mode.

20. A front-end according to claim 18 , wherein the feedback control circuit accesses the voltage sensor and current adjustor in a differential mode.

21. A front-end of a first common-mode voltage circuit that is DC-coupled to an output of a second common-mode voltage circuit, comprising:
a first resistive element, having a resistivity between a first end that is DC-coupled to the second circuit and a second end that is DC-coupled to an input of the first circuit, for accepting a programmable current passing therethrough to impose a voltage thereacross, that varies in direction and amplitude according to the current value;
a voltage sensor for sensing a difference between a DC voltage at the second end of the first resistive element and a desired reference voltage of the first circuit;
a current adjustor for adjusting a direction and amplitude of the programmable current so that the voltage of the first circuit matches the desired reference voltage; and
a current canceller comprising a second resistive element connected at a first end to the output of the second circuit, the current canceller for sensing the programmable current and for generating a current of equal amplitude through the second resistive element and away from the output of the second circuit.

22. A front-end according to claim 21 , wherein the first circuit is a receiver circuit.

23. A front-end according to claim 21 , wherein the second circuit is a transmitter circuit.

24. A front-end according to claim 23 , wherein the second resistive element is a resistor.

25. A front-end according to claim 23 , wherein the current canceller senses the programmable current by sensing a voltage at each end of the first resistive element and determining a first difference therein that is proportional to the programmable current by a known resistivity of the first resistive element.

26. A front-end according to claim 25 , wherein the current canceller senses the current generated through the second resistive element by sensing a voltage at each end of the second resistive element and determining a second difference therein that is proportional to the generated current by a known resistivity of the second resistive element.

27. A front-end according to claim 26 , wherein the current canceller comprises a feedback loop the first and second differences as inputs and for generating as an output, the current passing through the second resistive element.

28. A front-end according to claim 27 , wherein the feedback loop adjusts the current generated until the second difference approaches the first difference.

29. A front-end according to claim 27 , wherein the known resistivity of the first resistive element is equal to the known resistivity of the second resistive element.

30. A front-end according to claim 27 , wherein the feedback loop comprises an op-amp.

31. A front-end according to claim 30 , wherein the op-amp has first and second differential inputs for accepting the first and second differences.

32. A front-end according to claim 27 , wherein the feedback loop comprises an error generator.

33. A front-end according to claim 32 , wherein the error generator accepts as inputs the first and second differences.

34. A front-end according to claim 32 , wherein the feedback loop comprises a plurality of analog-to-digital converters (ADCs) for generating digital inputs to the error generator.

35. A front-end according to claim 32 , wherein the feedback loop comprises a proportional and integral (PI) filter for converting an output of the subtractive adder to a digital current value.

36. A front-end according to claim 35 , wherein the feedback loop

Assignees

• Lacroix Marc-Andre
• Huawei Tech Co Ltd

Inventors

• Lacroix Marc-Andre

Classifications

• H04B3/548 Primary

  the power on the line being DC (arrangements for feeding power H04L12/10; extracting feeding power from signals H04L25/02) · CPC title

• H04B1/16 Primary

  Circuits · CPC title